Terazosin, especially in its salt forms, is a well-known medicament which is useful in the treatment of hypertension and benign prostatic hyperplasia. For example, U.S. Pat. No. 4,026,894 discloses the hydrochloride salt of terazosin as well as its use in pharmaceutical formulations used for the treatment of hypertension, and U.S. Pat. No. 4,251,532 discloses the compound terazosin hydrochloride dihydrate and its use as a pharmaceutical active ingredient.
The U.S. Food and Drug Administration (FDA) first approved terazosin hydrochloride dihydrate for sale in the United States in 1987 as a tablet formulation which was marketed by Abbott Laboratories under the tradename HYTRIN.
U.S. Pat. No. 5,294,615 describes a soft gelatin capsule dosage form containing terazosin hydrochloride in a non-aqueous liquid carrier and indicates that polyethylene glycol is a preferred non-aqueous liquid carrier. In 1994, the FDA approved a soft gelatin capsule formulation containing the active ingredient suspended in a non-aqueous liquid carrier composed primarily of polyethylene glycol with some glycerine present.
The present invention relates to the surprising discovery that a stable, therapeutic equivalent of known liquid-filled capsule dosage forms of terazosin hydrochloride is prepared simply and effectively by replacing the liquid carrier with a solid carrier. Thus, the present invention relates to solid-filled terazosin hydrochloride capsules which are stable under accelerated conditions and which are therapeutic equivalents of the liquid-filled capsule dosage forms.
As therapeutic equivalents, the inventive solid-filled terazosin hydrochloride capsules are surprisingly bioequivalent to the FDA approved liquid-filled terazosin hydrochloride capsules. It is a great advantage that the inventive formulations are bioequivalent to the FDA approved liquid-filled terazosin hydrochloride capsules because the inventive formulations can be marketed as generic equivalents of the approved product without performing new safety and efficacy studies, which add considerably to the cost of obtaining FDA approval to market a drug product.